Error in R2 Datatypes

Jun 17, 2014

Today, Rick Geimer and Austin Kreisler discovered a rather egregious error in the Data Types R2 specifications. The ISO data types say:

This specification defines the following extensions to the URN scheme:

hl7ii – a reference to an II value defined in this specification. The full syntax of the URN is urn:hl7ii:{root}[:{extension}] where {root} and {extension} (if present) are the values from the II that is being referenced. Full details of this protocol are defined in the HL7 Abstract Data Types Specification

Reference: Section 7.6.2.7 of the ISO Data types

However, if you look through the Abstract Data Types R2 for information about this, you won’t find anything about hl7ii. But there is this, in section 4.13.1.1:

The scheme hl7-att is used to make references to HL7 Attachments. HL7 attachments may be located in the instance itself as an attachment on the Message class, or in some wrapping entity such as a MIME package, or stored elsewhere.The following rules are required to make the hl7-att scheme work:

  1. Attachments SHALL be globally uniquely identified. Attachment id is mandatory, and an ID SHALL never be re-used. Once assigned, an attachment id SHALL be accosiated with exactly one byte-stream as defined for ED.data.
  2. When receiving an attachment, a receiver SHOULD store that attachment for later reference. A sender is not required to resend the same attachment if the attachment has already been sent.
  3. Attachment references SHALL be resolved against all stored attachments using the globally unique attachment identifier in the address.

(p.s. references are behind HL7 registration wall, but are free)

These are meant to be the same thing, but they are named differently: urn:hl7ii:… vs hl7-att:…

I guess this will have to be handled as a technical correction to one of the two specifications. I prefer urn:hl7ii:.

Comments welcome.